Paper feeder, image forming apparatus provided with the same and paper feeding method

Abstract

When two or more sheets of paper P are fed in an overlapped manner to a nip where a paper feed roller and a separation roller are in pressure contact with each other, a sub-CPU of a sheet feeding unit rotates the paper feed roller in a paper feeding direction and rotates the separation roller in a direction opposite to the feeding direction, so as to separate overlapping, and thereafter, it rotates the paper feed roller and the separation roller again in the feeding direction.

1. A paper feeder feeding sheets of paper contained stacked in a paper feed cassette one by one from an uppermost layer to a paper feed path, comprising:
 a paper feed roller and a separation roller forming a pair in a vertical direction and by rotating in a paper feeding direction, passing said sheet of paper through a first nip where the rollers are in pressure contact with each other; 
 a first paper sensor arranged on a downstream side of said paper feed roller in the feeding direction; 
 a pair of conveyor rollers forming a pair in the vertical direction, arranged on the downstream side of said paper feed roller and said separation roller in the paper feeding direction, and by rotating in the feeding direction, passing said sheet of paper through a second nip where the pair of conveyor rollers are in pressure contact with each other; 
 a second paper sensor arranged on a downstream side of said pair of conveyor rollers in the feeding direction; 
 a first controller causing said paper feed roller to rotate in the feeding direction and causing said separation roller to rotate in a direction opposite to the feeding direction, when said first paper sensor detects said paper and a plurality of said sheets of paper exist at said first nip; and 
 a second controller causing said paper feed roller and said separation roller to rotate in the feeding direction, when said paper is once detected but thereafter no longer detected by said first paper sensor, and said paper is not detected by said second paper sensor within a prescribed time period. 
 
     
     
       2. The paper feeder according to  claim 1 , further comprising
 a third controller causing said paper feed roller and said separation roller to rotate in the feeding direction, when said paper is not detected by said first paper sensor. 
 
     
     
       3. The paper feeder according to  claim 2 , further comprising
 a fourth controller causing said paper feed roller and said separation roller to repeat rotation in the feeding direction for a prescribed number of times, by controlling said second controller. 
 
     
     
       4. The paper feeder according to  claim 3 , further comprising
 a fifth controller stopping an operation of said paper feeder, after said second controller caused said paper feed roller and said separation roller to repeat rotation in the feeding direction for the prescribed number of times. 
 
     
     
       5. The paper feeder according to  claim 4 , further comprising:
 a display unit for displaying information to be notified to a user; and 
 a sixth controller causing said display unit to display an indication of paper failure, in response to said fifth controller stopping operation of the paper feeder. 
 
     
     
       6. The paper feeder according to  claim 1 , wherein
 said second controller sets rotation speed of said paper feed roller slower than rotation speed before detection of the paper by said first paper sensor. 
 
     
     
       7. An image forming apparatus, comprising:
 a paper feeder feeding sheets of paper contained stacked in a paper feed cassette one by one from an uppermost layer to a paper feed path, including 
 a paper feed roller and a separation roller forming a pair in a vertical direction and by rotating in a paper feeding direction, passing said sheet of paper through a first nip where the rollers are in pressure contact with each other, 
 a first paper sensor arranged on a downstream side of said paper feed roller in the feeding direction, 
 a pair of conveyor rollers forming a pair in the vertical direction, arranged on the downstream side of said paper feed roller and said separation roller in the paper feeding direction, and by rotating in the feeding direction, passing said sheet of paper through a second nip where the pair of conveyor rollers are in pressure contact with each other, 
 a second paper sensor arranged on a downstream side of said pair of conveyor rollers in the feeding direction, 
 a first controller causing said paper feed roller to rotate in the feeding direction and causing said separation roller to rotate in a direction opposite to the feeding direction, when said first paper sensor detects said paper and a plurality of said sheets of paper exist at said first nip, and 
 a second controller causing said paper feed roller and said separation roller to rotate in the feeding direction, when said paper is once detected but thereafter no longer detected by said first paper sensor, and said paper is not detected by said second paper sensor within a prescribed time period; and 
 an image forming unit forming a desired image on a sheet of paper fed to said paper feed path. 
 
     
     
       8. A paper feeding method of feeding sheets of paper contained stacked in a paper feed cassette one by one from an uppermost layer to a paper feed path, comprising the steps of:
 rotating, in a paper feeding direction, a paper feed roller and a separation roller forming a pair in a vertical direction to form a first nip, and thereby passing said sheet of paper through said first nip; 
 rotating, in the paper feeding direction, a pair of conveyor rollers arranged on a downstream side of said paper feed roller and said separation roller in the feeding direction and forming a pair in the vertical direction to form a second nip, and thereby passing said sheet of paper through said second nip; 
 rotating said paper feed roller in the feeding direction and rotating said separation roller in a direction opposite to the feeding direction, when a first paper sensor, provided on the downstream side of said paper feed roller in the feeding direction, detects said paper and a plurality of said sheets of paper exist at said first nip; and 
 rotating said paper feed roller and said separation roller in the feeding direction, when said paper is once detected but thereafter no longer detected by said first paper sensor, and said paper is not detected by a second paper sensor, arranged on the downstream side of said conveyor roller pair in the feeding direction, within a prescribed time period. 
 
     
     
       9. A paper feed program, causing, when executed by a computer, said computer to execute a paper feeding method of feeding sheets of paper contained stacked in a paper feed cassette one by one from an upper most layer to a paper feed path, said paper feeding method including the steps of:
 rotating, in a paper feeding direction, a paper feed roller and a separation roller forming a pair in a vertical direction to form a first nip, and thereby passing said sheet of paper through said first nip; 
 rotating, in the paper feeding direction, a pair of conveyor rollers arranged downstream of said paper feed roller and said separation roller in the feeding direction and forming a pair in the vertical direction to form a second nip, and thereby passing said sheet of paper through said second nip; 
 rotating said paper feed roller in the feeding direction and rotating said separation roller in a direction opposite to the feeding direction, when a first paper sensor, provided on the downstream side of said paper feed roller in the feeding direction, detects said paper and a plurality of said sheets of paper exist at said first nip; and 
 rotating said paper feed roller and said separation roller in the feeding direction, when said paper is once detected but thereafter no longer detected by said first paper sensor, and said paper is not detected by a second paper sensor, arranged on the downstream side of said pair of conveyor rollers in the feeding direction, within a prescribed time period. 
 
     
     
       10. A computer-readable recording medium recording a paper feed program, causing, when executed by a computer, said computer to execute a paper feeding method of feeding sheets of paper contained stacked in a paper feed cassette one by one from an uppermost layer to a paper feed path, said paper feeding method including the steps of:
 rotating, in a paper feeding direction, a paper feed roller and a separation roller forming a pair in a vertical direction to form a first nip, and thereby passing said sheet of paper through said first nip; 
 rotating, in the paper feeding direction, a pair of conveyor rollers arranged downstream of said paper feed roller and said separation roller in the feeding direction and forming a pair in the vertical direction to form a second nip, and thereby passing said sheet of paper through said second nip; 
 rotating said paper feed roller in the feeding direction and rotating said separation roller in a direction opposite to the feeding direction, when a first paper sensor, provided on the downstream side of said paper feed roller in the feeding direction, detects said paper and a plurality of said sheets of paper exist at said first nip; and 
 rotating said paper feed roller and said separation roller in the feeding direction, when said paper is once detected but thereafter no longer detected by said first paper sensor, and said paper is not detected by a second paper sensor, arranged on the downstream side of said pair of conveyor rollers in the feeding direction, within a prescribed time period.